Recently, camera devices, such as digital still cameras, incorporating solid-state image sensors have been popular. This tendency of the market demand has been followed by the performance improvement and downsizing of optical systems, and more compact camera systems have rapidly become commercially available. Optical systems in such camera systems are of higher-performance oriented and increasingly downsizing oriented design to meet the market demands for zoom lens optical systems with a shortened entire length and for lens barrels with a reduced diameter. Especially, it is highly desired that optical systems, such as tele-photographing zoom lenses, having an increased focal length should be of more enhanced performance and reduced dimensions.
One prior art highly variable power compact zoom lens, which satisfies the demands of higher-performance and reduced dimensions, comprises the foremost or first lens group G1 of positive refractive power located the closest to an object, the succeeding or second lens group G2 of negative refractive power, the third lens group G3 of positive refractive power, and the fourth lens group L4 of positive refractive power located the closest to the imaging plane, and such a prior art zoom lens meets the requirements as defined in the following formula:12<Lt/(Ft/Fw)<15where Lt is an entire length of the optical system (a distance from the front surface of the front lens piece the closest to the object to the imaging plane) when the zoom lens is taking a telephoto position, Ft is a focal length of the optical system as a whole when the zoom lens is taking a telephoto position, and Fw is a focal length of the optical system as a whole when the zoom lens is taking a wide-angle position (e.g., see Patent Document 1 listed below).